The present invention relates to a sewing machine for automatic thread take-up and threading. More specifically, the present invention relates to a sewing machine in which a needle thread is automatically taken up by a needle take-up and threaded through an eye of a needle prior to sewing operation.
Prior-art sewing machines can automatically perform the thread take-up operation of a needle thread by a thread take-up (hereafter referred to as "thread up operation") or threading operation to the eye of a needle (hereafter referred to as "threading operation") prior to sewing.
For example, Japan Published Unexamined Patent Application H1-113092 discloses a sewing machine, where a hook for threading is driven to pass through the eye of a needle by means of an air cylinder and an operator manually hangs a needle thread on the hook. Thus, the threading operation can be executed somewhat automatically.
On the other hand, in a sewing machine proposed in Japan Published Examined Utility Model Application S63-228, the thread take-up operation is executed automatically. A needle thread strung intersecting an area where a thread take-up moves is pushed out when the thread take-up swings down and then is picked up by a hook at an end of the thread take-up when the thread take-up swings up. The needle thread needs to be strung with appropriate tensile strength so as not to be slackened off when pushed out by the thread take-up.
The combination of the above-mentioned two sewing machines would seem to produce a sewing machine which can automatically perform both the thread take-up operation and the threading operation. Such a combined sewing machine, however, would have the following problems. When the needle thread is caught by the thread take-up, the needle thread is extracted from the upstream side above the thread take-up, namely from a bobbin, and also from the downstream side. Accordingly, the needle thread at the downstream side below the thread take-up has to be about 12 cm or longer. Consequently, when the threading operation is executed before the thread take-up operation, the needle thread of about 12 cm or longer must be passed through the eye of the needle, which cannot be automatically executed because of the extreme length. Accordingly, before the thread take-up operation, the operator must pull out the needle thread about 12 cm or longer which is automatically prepared beyond the eye of the needle about several millimeters through about several centimeters. In addition, he must hold onto the free end of the needle thread by hand because the thread take-up swinging up at high speed would otherwise pull the needle thread out of the eye.
Another problem exists when the thread take-up operation is executed before the threading operation. Before the thread take-up swings down, the needle thread has to be strung with appropriate tensile strength so as to cross the thread take-up moving area and be slackened more than 12 cm such that the end of the needle thread does not get out of place when the thread take-up swings down. Further, the needle thread must be prepared for the threading operation at the downstream side below the thread take-up after the thread take-up operation has finished. Accordingly, the thread take-up operation and the threading operation are separately performed, and the operator must prepare the needle thread twice for the thread take-up operation and the threading operation.
Therefore, the object of this invention is to provide a sewing machine for automatic thread take-up and threading that can perform the thread take-up operation and the threading operation without failure after simple preparation of the needle thread.
Other objects and benefits of the invention will become apparent from the detailed description which follows hereinafter when taken in conjunction with the drawing figures which accompany it.